I second the notion of "sometimes the snake just decides to have a bad shed." I keep my 1.1 pair in identical cages, exact same temps, humidity, etc, and the last time my female she, she rubbed off half of her head, some on her belly, and just left the rest.

I was like HELLO YOU AREN'T DONE! I gave her the rest of the night to finish and in the morning it was still the same. I used the remedies listed above by adam and got the rest off.

Last night my male shed. Perfect one-piece. I didn't even know he was in shed. O well!